The following description is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art.
Computational methods for simulating reverberant environments are well developed [2], and find application fields ranging from virtual reality to music recording and film audio production. Room acoustics is an approximately linear and time-invariant process, and one widely used method for room acoustics simulation is convolution with a measured or synthesized room impulse response [3, 4]; see FIG. 1. Another commonly used approach is to delay the input by different, incommensurate amounts, and filter, mix, and feedback the delayed signals in a process akin to the generation of an increasingly dense set of reflections that develop in a room. The feedback delay network (FDN), shown in FIG. 2 is an example of this approach, and provides separate mechanisms to control the decay time as a function of frequency and the rate of echo density increase [5]. A third approach decomposes the room response into a parallel set of mode responses, as shown in FIG. 3, with each mode response corresponding to a resonance of the room and characterized by an amplitude, resonant frequency, and decay time [6, 7].
In a number of scenarios, it is desired to manipulate or control the perceived size of a given acoustic space. In a virtual reality or film audio setting, for instance, the size of the room might be changing over time, and it is desired that the acoustics of the space change accordingly. In a music recording, performance, or composition environment, different sizes of acoustic space convey different musical impressions, and it is desired to have a palette of room size options associated with a given room response for artistic purposes.
Larger spaces tend to be more reverberant and “darker” than smaller ones, but there doesn't seem to be available a systematic way to manipulate the perceived size associated with a given room response. Additionally, changes in controls driving common reverberators often produce zippering and other unwanted artifacts in the output while the controls are slewed. Finally, changes over time in the size of an actual room can produce Doppler shifts that, while appropriate for virtual reality applications, are undesired in musical applications in which pitches can be detuned.
Thus, there is a need for an artificial reverberator that provides control over the perceived size of the simulated space. There is also a need for the perceived room size to vary smoothly over time in response to a smoothly changing room size control. In addition, there is a need for a room size control that doesn't produce Doppler shifts in response to a continuously changing room size.